A conventional prosthesis socket is generally circular in cross section and consists of an inner socket to interface with the user's skin and an outer socket over it that incorporates the mechanisms that comprise an additional structure, for example, an artificial joint or a device to function as a foot or gripping device. The inner and outer sockets may be separate structures or may consist of a single unit.
The term “interface” is used by some in the field as a synonym for socket, but in this disclosure the term “socket” is used exclusively.
The term “cast” conventionally refers to a thin layer of wet plaster impregnated gauze wrapped around a residual limb and the surrounding body parts and then permitted to harden to reproduce the shape of the limb. While the plaster is hardening, pressure from the hands of the plaster technician often modifies the shape to accommodate the underlying boney anatomy.
The term “positive model” refers to the plaster model that results from filling a cast with plaster or similar material. Modifications by adding and subtracting plaster are made to the positive model before its outer surface is used to define the shape of the user's socket.
The term “check socket” is a temporary socket made using the positive model and used to test whether the modifications have had the desired effect on the fit of the resulting socket.
Historically the socket for prosthetic applications has been a generally cylindrical socket that merely surrounds the remaining limb part with some contouring of the proximal brim so that it will accommodate the shape of the next proximal joint or body part. Typically, this socket is made by taking a plaster cast over the limb and filling it with plaster to form a positive model of the limb. Minor changes are made to this shape to conform to boney prominences. When the positive model is used to create a socket by laminating or thermoforming a layer of plastic over the model, the resulting socket primarily encapsulates the limb part.
Some improvements have been made in the conventional socket. In particular, many technicians replace the fully encapsulating outer socket with a frame having one or more openings. This change is accompanied by making the inner socket of a flexible material. The resulting frame-style design usually is more comfortable. New materials such as carbon fiber composites add rigidity where needed especially in open frame designs. New flexible materials allow the socket wall to flex in some areas for comfort. Even when these newer flexible materials are used, the soft liner still fully encapsulates the remaining limb as conventionally done and, thus, provides a compressive or elastic force to all of the limb's soft tissue.
Conventional laminations over a positive model work best when the surfaces of the positive model are convex facing outward, following the general contours of the outside surface of the limb.
Fitting a conventional socket is a multistage process involving creating a cast, waiting for it to dry, making a positive model of the initial cast, waiting for it to dry, creating a test socket, waiting for it to dry, adjusting the positive model, and then finally creating the final socket. To tailor further the fit to the patient, the castings removed from each mold usually must be further shaped, often by hand, to achieve the comfort and wearability required by the user.
Thus, the user of these conventional sockets is faced with the disadvantage of spending an extensive period of time being fit with the socket, and may need to visit the offices of the socket designer several times over the course of having the socket fit. A secondary disadvantage of this conventional method of making the socket is its expense due to the need for a skilled professional to handcraft the socket during the time intensive fitting process.